ATA8743 ATMEL Corporation, ATA8743 Datasheet - Page 165

• Manufacturer Part Number: ATA8743
• Manufacturer: ATMEL Corporation

25.8.3
25.9
Table 25-2.
9152A–INDCO–07/09
Temperature / °C
Voltage / mV
Temperature Measurement
Bipolar Differential Conversion
Temperature vs. Sensor Output Voltage (Typical Case)
than the voltage of the negative pin or otherwise the voltage difference is saturated to zero. The
result is presented in one-sided form, from 0x000 (0d) through 0x3FF (+1023d). The GAIN is
either 1x or 20x.
If differential channels and a bipolar input mode are used, the result is
where V
and V
0x200 (-512d) through 0x1FF (+511d). The GAIN is either 1x or 20x. Note that if the user wants
to perform a quick polarity check of the result, it is sufficient to read the MSB of the result (ADC9
in ADCH). If the bit is one, the result is negative, and if this bit is zero, the result is positive.
As default the ADC converter operates in the unipolar input mode, but the bipolar input mode
can be selected by writing the BIN bit in the ADCSRB to one. In the bipolar input mode two-sided
voltage differences are allowed and thus the voltage on the negative input pin can also be larger
than the voltage on the positive input pin.
The temperature measurement is based on an on-chip temperature sensor that is coupled to a
single ended ADC8 channel. Selecting the ADC8 channel by writing the MUX5:0 bits in ADMUX
register to “100010” enables the temperature sensor. The internal 1.1V reference must also be
selected for the ADC reference source in the temperature sensor measurement. When the tem-
perature sensor is enabled, the ADC converter can be used in single conversion mode to
measure the voltage over the temperature sensor. The measured voltage has a linear relation-
ship to the temperature as described in Table 51. The voltage sensitivity is approximately 1 mV /
°
gap is always calibrated and its accuracy is only guaranteed between 1.0V and 1.2V
The values described in
variation the temperature sensor output voltage varies from one chip to another. To be capable
of achieving more accurate results the temperature measurement can be calibrated in the appli-
cation software. The software calibration requires that a calibration value is measured and
stored in a register or EEPROM for each chip, as a part of the production test. The software cal-
ibration can be done utilizing the formula:
where ADCn are the ADC data registers, k is a fixed coefficient and T
sor offset value determined and stored into EEPROM as a part of the production test.To obtain
best accuracy the coefficient k should be measured using two temperature calibrations. Using
offset calibration, set k = 1.0, where k = (1024*1.07mV/°C)/1.1V~1.0 [1/°C].
C and the accuracy of the temperature measurement is +/-
REF
243 mV
-40°C
POS
the selected voltage reference. The result is presented in two’s complement form, from
is the voltage on the positive input pin, V
Table 25-2 on page 165
ADC
T = {[(ADCH << 8) | ADCL] - TOS} / k
314 mv
+25°C
=
-------------------------------------------------------
V
POS
–
V
V
REF
NEG
are typical values. However, due to the process
512
NEG
380 mV
the voltage on the negative input pin,
+85°C
GAIN
10°
C after offset calibration. Band-
OS
is the temperature sen-
ATA8743
424 mV
+125°C
165